Ex-Labour minister Ivan Lewis has quit the party as he expressed doubts about Jeremy Corbyn's willingness to fight antisemitism.
The Bury South MP resigned from Labour on Thursday with "great sadness", but told Mr Corbyn in a letter: "All too often you have been unwilling to condemn those whose hatred of Israel becomes Jew hatred."
Mr Lewis, 51, has been suspended by Labour since November last year amid an investigation into allegations of sexual harassment.
He has denied ever making non-consensual sexual comments or sexual advances towards women.
Among the allegations, it was reported last year that Mr Lewis touched a woman's leg and invited her to his house at a Labour Party event in 2010, when she was 19.
Sky News understands Mr Lewis was recently informed a date for his hearing with Labour's quasi-judicial disciplinary body would be set in the New Year.
His resignation means that hearing will now not take place and the investigation into the MP cannot be concluded.
A party source said: "Ivan was under investigation for alleged sexual harassment. His resignation means the complainants have been denied a hearing."
In his resignation letter to Mr Corbyn, Mr Lewis claimed he had never been interviewed about the complaints made against him.
He also hit out at an "unnecessary and politically motivated delay" in dealing with his case, despite Labour officials being "fully aware of the impact the situation was having on my mental health".
"Emails the party were forced to make available to me show clearly the party could have moved forward with the disciplinary process from April but chose not to for political reasons," he wrote.
Mr Lewis revealed he had previously considered resigning in October, after a summer-long antisemitism row hit Labour, as he "could no longer reconcile my Jewish identity and current Labour politics".
He claimed, at this point, a "sudden attempt" was made to move forward his disciplinary process, which came at a point when "political control" of the body investigating Mr Lewis had passed to "supporters" of Mr Corbyn.
"This is a process that is flawed and subject to political manipulation," Mr Lewis wrote.
"I have made it clear I strongly refute the charges which have been made and I am willing to cooperate with a truly independent process."
Mr Lewis told Mr Corbyn it is "for others to determine whether you are antisemitic", but he claimed it is "clear" the Labour leader and his key aide Seamus Milne "do not believe in the right of the Jewish people to self-determination in their own state".
He added: "You should be honest and acknowledge your preference is that there should only be a state of Palestine."
Attacking Mr Corbyn's "anti-Western world view", Mr Lewis claimed the Labour leader's "long-standing preferences are for the values of Putin's Russia and the Islamist fundamentalism of Iran".
He also claimed Mr Corbyn has "discomfort" over Brexit as a "lifelong eurosceptic" leading an "overwhelmingly pro-European" party.
Labour sources expressed bemusement at "false and bizarre allegations" in Mr Lewis's letter, stressing Mr Corbyn is committed to a two-state solution in securing peace in the Middle East.
They also denied any "political involvement" in the disciplinary processes used to investigate the claims against Mr Lewis, which are "entirely separate" from the party's leadership.
Mr Lewis served as a minister in both Tony Blair and Gordon Brown's governments, while he was also a member of former Labour leader Ed Miliband's shadow cabinet.
He sought to become Labour's mayoral candidate in Greater Manchester in 2016 but the party instead chose Andy Burnham.
Mr Lewis has vowed to "continue to fight for local people" in Bury South as an independent MP.
In response to Mr Lewis's resignation, a Labour Party spokesperson said: "Jeremy Corbyn thanks Ivan for his service to the Labour Party.
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"The Labour Party takes all complaints of sexual harassment extremely seriously, which are fully investigated in line with our rules and procedures and appropriate disciplinary action taken.
"This case was referred to a full hearing of Labour's National Constitutional Committee. The process is the same for everyone."